Ab Initio Study of Hydrogen Niobate HNbO3: Structural, Thermodynamic, Dielectric, and Optical Properties

Using first-principles calculations, we study the ground-state structure of bulk proton-exchanged lithium niobate, which is also called hydrogen niobate and is widely used in waveguides. Thermodynamics helps to establish the most favorable nonpolar surface as well as the water-deficient and water-rich phases under different ambient conditions, which we refer to as dehydrated and rehydrated phases, respectively. We compute the low-frequency dielectric response and the optical refractive indices of hydrogen niobate in different phases. The dielectric constant is greatly enhanced compared to lithium niobate. At shorter wavelengths, the refractive indices vary between each phase and have a sharp contrast to lithium niobate. Our study characterizes the structures and thermal instabilities of this compound and reveals its excellent dielectric and optical properties, which can be important in the future application in waveguides.

Automated summary

Using first-principles calculations, this study investigates the ground-state structure, dielectric response, and optical properties of bulk proton-exchanged lithium niobate, a compound widely used in waveguides. Different ambient conditions result in the formation of dehydrated and rehydrated phases, which exhibit distinct dielectric constants and refractive indices compared to lithium niobate. The findings provide valuable insights into the structural and thermal characteristics of hydrogen niobate and its potential applications in waveguide devices.